1. Field of the Invention
This invention relates to a calibrator and, more particularly, to a wavelength calibration solution.
2. Description of the Prior Art
Frings et al. (1) report that the percentage of quantitative analyses performed in the clinical laboratory that involve spectrophotometry or colorimetry was estimated in 1969 to be possibly more than 95% (2). Most laboratories continue to rely heavily upon spectrometers or spectrophotometers for the majority of their analyses. Maintenance of properly functioning spectrometers and spectrophotometers is an obvious prerequisite to the assurance of accurate analytical results. Moreover, the increased regulation of clinical laboratory by governmental and professional agencies mandates that laboratory personnel periodically verify that a given spectrometer or spectrophotometer is functioning properly. By periodically inspecting spectrometric and spectrophotometric functions, subtle or gradual degradations in performance can be detected before they significantly affect analytical results. As a minimum, these inspections should include, inter alia, a check of wavelength calibration.
With respect to wavelength calibration, periodic checks are necessary to insure that the instrument wavelength accurately reflects the wavelength of energy passing through the exit slit of the monochromators. Several methods are available for checking wavelength accuracy of a spectrometer or a spectrophotometer. These methods include (a) replacing the source lamp with a radiant energy source which has strong emission lines at well defined wavelengths; (b) using rare earth glass filters; and (c) using solutions such as samarium oxide. Irrespective of the method of wavelength calibration, calibration at more than one wavelength is required for proper calibration of the instrument.
In general, the wavelength calibration solution technique involves measuring absorbance (A) or percent transmittance (%T) of the wavelength calibration check solution versus a blank (e.g., water) at more than one wavelength.
Prior art solutions employed to check wavelength accuracy have characteristic wavelength peaks which are not sufficiently separated to enable one to calibrate the instrument over a sufficiently wide spectral range. For example, holmium oxide has characteristic peaks at 536.4 nm, 418.5 nm, and 360.8 nm. In addition, the peaks at 418.5 and 536.4 nm are not easily identifiable due to lack of peak intensity.
In contrast, it would be very desirable to employ a solution with at least two very easily identifiable, sharp peaks which are separated by over 100 nms.